CHAPTER III: RESULTS Species Occurrence and Habitat Relationships The geological, topographic, and climatic diversity of Nevada County contribute to its high plant and animal diversity. The county contains a complete east-west transect of the northern Sierra, from just above the Central Valley grasslands to the Great Basin vegetation on the Nevada border. The extent, elevation range, and numbers of Redlist and Yellowlist plants and animal species with documented occurrence in each of Nevada County’s 27 large-patch ecosystems are summarized in Table 3-1. Discussions of plant and animal occurrence in large-patch ecosystems of the county are provided in the following sections. Plant Diversity Nevada County supports a rich flora, with 1,814 taxa of California’s approximately 7,000 species, subspecies, and varieties documented within the county’s boundaries (Appendix I, CalFlora 2002). This represents about 26% of the California flora growing on <0.6% of the state’s total land area. A total of 115 plant families, representing 582 genera, are included in the flora of Nevada County. Of the 1,814 plant taxa found in Nevada County, about 19% are naturalized non-native species. Native taxa are those believed to have existed in California before initial visitation and colonization by Europeans (Hickman 1993). Ferns and fern-allies make up a little over 2% of the local flora; gymnosperms (conifers) total only 1% of the total number of taxa. Flowering plants make up over 96% of the taxa, which includes 22% monocots (i.e., grasses and lilies) and 74% dicots (other flowering plants). Fifty-six species of Redlist or Yellowlist plants have documented occurrences in Nevada County (Appendix II). Nevada County spans a region from the eastern edge of the Sacramento Valley and lower Sierra foothills to the Sierra crest and east to the Nevada state line in a transitional zone between the Great Basin and Sierra Nevada floristic provinces (Hickman 1993). Nearly all Sierra Nevada ecosystems are found here, except Central Valley perennial grasslands, and true Alpine habitats (True 1973). Elevations range from approximately 250 feet elevation at Parks Bar on the Yuba River mainstem to the Subalpine ecosystems at 9,143 feet on the summit of Mt. Lola (Table 3-1). Although Nevada County lacks a comprehensive floristic treatment, a checklist of vascular plants was issued in 1973 by the California Academy of Sciences (True 1973). The list was authored by a local botanist, the late Gordon True, who owned a small dairy ranch along McCourtney Road in the 1960’s and early 1970’s. His checklist was based on vouchered specimens collected by True and other notable botanists such as Peter Raven and John Thomas Howell. The majority of his specimens are housed at the California Academy of Sciences and the U.C. Berkeley and Jepson herbariums (CalFlora 2002). The other primary source for information on the Nevada County flora is the electronic database of the U.C. Berkeley Digital Library Project- CalFlora Database. The database includes Nevada County specimens collected as early as the mid- to late 1800’s from explorers and plant collectors such as John Fremont and the Danish bookkeeper C.F. Sonne. Unique Features of Nevada County Plant Populations The California Environmental Quality Act, Appendix G, Initial Study Environment Checklist, requires that environmental analyses evaluate the impact of projects on locally significant plants. Both plants and plant communities can be considered significant if their local occurrence is on the outer limits of known distribution, a range extension, a rediscovery, or rare or uncommon in a local context. A number of Nevada County plant species and plant communities are significant for these reasons. Nevada County is reported to be the southernmost extension of the global distribution of California pitcher plant, an unusual insectivorous plant (CalFlora 2002). The county is the northernmost limit of the Sierra Nevada distribution of whitebark pine, which makes its next appearance to the north on the highest peaks of the southern Cascade Range (Griffin and Critchfield 1976). Washoe pine is an uncommon species known from only a few occurrences in California between Modoc County and Mt. Rose, Nevada, including an unconfirmed report between Hobart Mills and Boca Reservoir (Griffin and Critchfield 1976). Clark’s ragwort and the Yellowlist long-petaled lewisia reach their northern limits in Nevada County. Another species, starved daisy, has a global distribution restricted to the higher elevations of Nevada and Placer counties (USDA Forest Service 2000, CalFlora 2002, CNDDB 2002). The Washington Ridge serpentines of Nevada County support the only Sierra Nevada occurrence of wedgeleaf violet, a species otherwise known only in northwestern California (True 1973). Some unusual and quite colorful plant associations are also found in the vernally wet habitats of some “lava caps” on the east and west slopes of the Sierra crest in the county. Nevada County is also the apparent California epicenter of the genus Carex (sedges), with more than 60 documented species and subspecies (True 1973). Other noteworthy disjunct occurrences are the small stands of knobcone pine in the Yuba River canyon and Red Dog areas; this species is common in the Cascade and Klamath ranges but quite uncommon in the Sierra Nevada (Griffin and Critchfield 1976). Although more common than other native cypresses, the global distribution of McNab cypress is limited to very widely scattered occurrences around the foothills surrounding the northern Sacramento Valley, primarily on serpentine or gabbrodiorite soils. A U.C. Davis researcher conducting a statewide study of serpentine diversity noted a particularly fine example of McNab cypress and leather oak chaparral on serpentine soils just south of the Sierra Nevada Memorial Hospital (Safford, pers. comm.). There are about 30 known occurrences of McNab cypress in the Sierra Nevada (CalFlora 2002). Many of the local occurrences of this species have been extirpated in Nevada County in the last few decades as the band of serpentine soils in or near the urban centers of Grass Valley and Nevada City have been converted to commercial, industrial, and residential development. Disjunct populations and localized plant occurrences may not be rare from a statewide perspective, but many are at high risk of regional extinction (Shapiro 2000). Many are “relicts,” populations left behind by climate change, persisting 10,000 to 20,000 years since the last Ice Age. Knobcone pines are a good example of this phenomenon. These disjunct occurrences are often genetically unique, due to long-term isolation from interbreeding with other populations. Rare, endemic, and disjunct taxa contribute to the diversity and uniqueness of a region’s flora (Shevock 1996). As more populations are lost, those remaining are increasingly isolated from one another, making them more vulnerable to extinction (Shapiro 2000). Poorly-Represented Species and Ecosystems Certain species and habitats are conspicuously absent from Nevada County. For example, Chamise-Redshank chaparral forms a nearly continuous band along the Sierra foothills and other parts of the state (Mayer and Laudenslayer 1988), but skips Nevada County entirely, with the exception of a reported small stand in the South Yuba River canyon (Olmstead pers. comm.). No carbonate or highly alkaline soils are found here (USDA Forest Service 1994, Brittan 1993), soils that are associated with many rare and endemic taxa in other regions. Nor does the county host any vernal pools of large size or significance, with the exception of a few pools in northeastern Nevada County (USFS 2000, CDFG website). Relatively little Fresh Emergent Wetland occurs in the foothill region of the county, and much of what does occur is dependent to some degree on intentional or unintentional releases or diversions of water by the Nevada Irrigation District (NID), including ditch leaks, manmade ponds, and irrigated pastures. Redlist Plants Only four plant species in Nevada County are “Redlisted” (i.e., listed as either Threatened or Endangered under the federal or state Endangered Species Acts [CNDDB 2002], Appendix II). Of these four listed species, the Tahoe yellow cress has probably been extirpated from the county. Tahoe yellow cress is documented by a single, historic collection in Truckee that is believed extirpated; little, if any, suitable habitat is still present for this species. The general vicinity of the collection area was searched in 1981, and no plants were observed (CNDDB 2002a). No surveys for this or any other Redlist or Yellowlist species were conducted for this study. The distribution and status of the remaining three Redlist species in Nevada County are discussed below. Scadden Flat Checkerbloom The entire global distribution of Scadden Flat checkerbloom is restricted to a few occurrences near Grass Valley. This species is not known to occur anywhere else in the world and is the one true endemic plant in Nevada County. This species is associated with the margins of Fresh Emergent Wetlands, and all populations are threatened to some degree by the invasive exotic Himalayan blackberry that consumes their habitats (CNDDB 2002a). Ponderosa pines are invading one of the marshes that contains this species. Site quality is reported to be good to poor among the three occurrences. CNDDB (2002b) indicates that one of the populations contains 2,000 plants, and a second contains only 10 plants; the size of the third population is not reported. Two of the occurrences are located within a highway right-of-way. Scadden Flat checkerbloom was first discovered by Gordon True and John Thomas Howell during True’s inventory of the Nevada County flora in the late 1960’s and early 1970’s (True 1973). The species was described after publication of the local checklist, and the first population was documented in 1985 (CNDDB 2002a). Stebbins’ Morning-Glory and Pine Hill Flannelbush Two other very rare Redlist species were previously only known from an area near Eldorado Hills and Cameron Park in El Dorado County until they were discovered southwest of Grass Valley.